The present invention relates to a method for the preparation of a semifinished product made of fiber material prior to a wet-pressing process, as well as to a preparation device for the preparation of the semifinished product made of fiber material prior to the wet-pressing process.
Methods for the preparation of semifinished products made of fiber material prior to wet-pressing processes are known in principle. For instance, so-called stacks that are embodied as multilayer fiber material are placed on preparation surfaces having a table form. Then, a flowable matrix material is introduced as a matrix substance from the upper side. Once the matrix substance has passed through and penetrated essentially all of the fiber material of the semifinished product, the saturated semifinished product may then be placed into the wet-pressing tool. There, the wet-pressing process is performed. However, in order to also be able to adequately saturate particularly thick semifinished products made of a plurality of layers of fiber material, it is not enough to introduce the matrix substance just from the upper side. On the contrary, for adequate saturation of the fiber material when the semifinished product is in multiple fiber layers, the semifinished product must be divided up. For instance, a maximum of approximately three to five-layer semifinished products are possible so that, for semifinished products that are thicker, individual semifinished product stacks must be placed on top of one another in a sandwich-like fashion. The matrix substance is introduced between the individual contact layers of the individual semifinished product stacks and may thus penetrate intimately into each semifinished product stack.
The tremendous complexity required for producing the individual semifinished product stacks is a drawback for the known methods. For instance, a plurality of individual semifinished product stacks, and not just one single semifinished product, must be produced for an entire structural component. The semifinished products are frequently unrolled from rolls of woven or nonwoven fabric made of fiber material, different layers being created from a plurality of rolls. This is followed by a cutting process to define the basic geometry of the semifinished product by cutting. If a plurality of two or even more different semifinished product stacks are needed to introduce the matrix substance in a sandwich-like fashion, at the least this also doubles the cutting process, the transport process, and all of the other steps starting from the production of the semifinished product all the way to saturating it with the matrix substance. If three or even more individual semifinished product stacks are needed, the complexity described consequently increases three-fold or more. This is critical in particular with respect to the time needed for production. The costs also rise sharply.
It is the object of the present invention to eliminate at least some of the drawbacks described in the foregoing. In particular, it is the object of the present invention to provide a method for the preparation of a semifinished product made of fiber material prior to a wet-pressing process, as well as to provide a corresponding preparation device that permits the flowable matrix substance to be introduced in a simple and cost-effective manner, even for thick semifinished products.
This and other objects are achieved according to the invention by a method for preparing a semifinished product made of fiber material, and having an upper side and an underside, prior to a wet-pressing process. The inventive method includes the following steps:                arranging a semifinished product made of fiber material with the underside on a preparation surface having a large number of suction apertures;        applying a negative pressure to the underside of the semifinished product via the suction apertures; and        introducing a flowable matrix substance via the upper side of the semifinished product.        
Thus, in one aspect of the invention, the material substance is introduced in a flowable manner exclusively via the upper side of the semifinished product. This makes it possible to do without the sandwich-like introduction of the matrix substance. In accordance with the invention, assistance is provided in order to ensure adequate penetration of the flowable matrix substance, regardless of the thickness of the semifinished product, that is, regardless of the number of layers of fiber material for the semifinished product. This assistance is provided by the negative pressure on the underside of the semifinished product.
If the semifinished product is arranged on the preparation surface with a large number of suction apertures, a negative pressure may then be applied to the underside. This negative pressure is generated, for example, using a compressor. By way of the negative pressure, a suction effect is created from the upper side of the semifinished product towards the underside. If a flowable matrix substance is now applied to the upper side of the semifinished product, in addition to the acting capillary forces and in addition to the acting gravity, this negative pressure assists the introduction of the flowable matrix substance. In other words, a fluid front for the matrix substance forms, which, and in addition to the previously mentioned effects, is also drawn through the thickness of the semifinished product by the negative pressure.
Naturally, a sensor element may be provided in the suction apertures to prevent the matrix substance from being introduced into these suction apertures. According to one advantageous development, it is also possible for a precise time control element to be used to define the point in time when the semifinished product has been completely penetrated by the flowable matrix substance. In the latter case, it would also be possible to do without complex sensor elements.
Proceeding from the preparation method in accordance with the present invention, the saturated semifinished product may now be placed, in a known manner, in a subsequent wet-press molding tool. The wet-pressing step for the wet-pressing process is then performed in the conventional and known manner.
The semifinished product in the context of the present invention is, in particular, a multilayer component, particularly preferably having a thickness that is relatively thick, in the range of approximately 2 to approximately 4 mm or more. A vacuum in the range of between approximately −0.2 bar and approximately −0.6 bar, in particular, is used for the negative pressure. Naturally, compressor devices may be used that can generate the negative pressure using a fluid-communicating connection to the suction apertures.
The semifinished product may also be called a stack, depending on how it is structured. The semifinished product may be produced in a known manner, for example, from rolls. Non-woven fabrics or woven fabrics or scrim made of the fiber material may be used.
In accordance with the inventive method, it is also possible, in particular, to saturate semifinished products that have complex geometries. Complex geometries shall be construed especially to include thick components and components with steep component edges. A steep component edge is defined by the side angle with respect to the horizontal in the wet-press molding tool, which is in the range between approx. 50° and approx. 90°.
After being introduced, the matrix substance is cured within the wet-pressing process. A resin substance, for instance, especially an epoxide resin, may be used as the matrix substance.
The method according to the invention may be refined in that arranged on the preparation surface is a stencil that covers sections of the suction apertures and, in particular, corresponds to the geometric shape of the semifinished product. A stencil shall be construed to be an element that is placed on the preparation surface. Correspondence with the geometric shape of the semifinished product shall be construed to mean, in particular, framing the semifinished product. In addition to framing, however, overhanging or overlapping the semifinished product is also possible. The stencil covers the suction apertures in a manner such that there are two options for how the stencil is embodied. First, it may be that the stencil is embodied impermeable to fluid, that is, the suction apertures at this location have no effect. However, it is also possible for the stencil to have its own interchangeable suction apertures that are distributed differently than the other suction apertures. Thus, the suction performance is changed so that the negative pressure may be varied. This supports the intentional application of negative pressure in individual sections of the semifinished product. However, the simplest solution is a stencil that is impermeable to fluid that is placed encircling the semifinished product. This makes it possible to use a large preparation surface, even for small semifinished products, without it being necessary to adjust the preparation surface. It is also possible to prepare a large number of semifinished products at the same time in the inventive manner.
Another advantage is obtained when, prior to the semifinished product being arranged on the preparation surface, an interchangeable insert adapted to the semifinished product is arranged on the preparation surface. In contrast to a stencil, an interchangeable insert shall be construed to mean a component that is inserted into the preparation surface, e.g. into a depression. The interchangeable insert may also be embodied both impermeable to fluid and having its own alternative apertures. Thus it may be adapted to the geometric shape of the semifinished product in the same manner as was described for the stencil. It is also possible for a defined negative pressure to be applied to individual sections of the semifinished product in a targeted manner using different interchangeable apertures.
Moreover, it is advantageous when the semifinished product made of fiber material is embodied as a multilayer semifinished product, especially with more than six layers. Thicknesses preferably in the range of approx. 2 mm to approx. 4 mm are provided. The thicker the semifinished product, the greater the advantage of the inventive method, because it is possible for the matrix substance to be introduced continuously from the upper side. However, the inventive method even provides advantages for thin semifinished products, since, in particular, it is possible to introduce the matrix substance more rapidly and thus a savings in time is achieved.
The method according to the invention may be refined in that at least sections of the semifinished product made of fiber material have the fibers in one of the following forms:                Fiber non-woven fabric,        Fiber woven fabric.        
Combinations of the possible forms of the previously mentioned, non-exhaustive list are possible in the context of the invention. Preferably, the individual fibers, that is, the fiber non-woven fabric or the fiber woven fabric, are arranged on roller tracks that may be placed one on top of the other, unrolled together and cut. This is a particularly cost-effective and simple way to produce the semifinished product.
The subject-matter of the present invention is likewise a preparation device for the preparation of a semifinished product made of fiber material prior to a wet-pressing process. Such a preparation device has a preparation surface for arranging the underside of the semifinished product. The inventive preparation device is distinguished in that the preparation surface has a large number of suction apertures that are configured for applying a negative pressure to the underside of the semifinished product. A compressor device that is in fluid-communicating connection with the suction apertures may be provided, for instance. The preparation surface may have corresponding fluid connectors for this purpose. The preparation device is used in particular for executing an inventive method such that the same advantages are attained using the inventive preparation device as have been explained in detail with respect to an inventive method.
The preparation device may be further developed in that an interchangeable insert and/or a stencil that covers the suction apertures of an interchangeable section is provided for at least one interchangeable section of the preparation surface. It is also possible to use combinations of interchangeable insert and stencil. Refer to the pertinent paragraphs relating to the method for definitions of the terms “interchangeable insert” and “stencil.” In both cases, interchangeable insert and/or stencil may be impermeable to fluid and may also be provided with their own interchangeable suction apertures. Naturally it may be provided that the interchangeable insert and/or the stencil may be fixed using fixing devices in order to maintain a defined position while the method is executed. In particular with large numbers of a defined shape for the semifinished product, such components in the form of interchangeable insert and/or stencil are advantageous because the speed when changing between two semifinished products may be increased significantly.
It is also advantageous when, in one embodiment of the preparation device, the interchangeable insert and/or the stencil has its own interchangeable suction apertures that are connected to the suction apertures of the preparation surface in a fluid-communicating manner. In particular, the interchangeable insert and/or the stencil may have a sub-volume over the surface so that the fluid-communicating connection is made available in a particularly cost-effective and simple manner. Thus closed and opened regions may be provided in a simple manner within the interchangeable insert and/or the stencil. The surface-area variation of the pressure or a pre-defined pressure distribution may thus be applied to the underside of the semifinished product in a particularly cost-effective and simple manner.
When providing interchangeable suction apertures, it may be advantageous for the suction apertures, and/or the interchangeable suction apertures in the inventive preparation device, to be distributed uniformly or essentially uniformly. This uniform or essentially uniform distribution provides for cost-effective and simple production of the component in question. It is also possible to attain in a uniform manner an essentially continuous fluid front when introducing the matrix substance. Naturally, uniformly distributed suction apertures may be combined with non-uniformly distributed interchangeable suction apertures and vice versa.
Alternatively, in an embodiment of the preparation device, it is also possible for the suction apertures and/or the interchangeable suction apertures to be distributed in a non-uniform manner in order to provide different suction sections. In this manner pressure distributions that extend two-dimensionally are possible. There may also be an adaptation to regions of the semifinished product that have different thicknesses so that the pressure distribution reflects the thickness distribution and thus an appropriately embodied fluid front is produced.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.